function y=Gurevich07(p,xdata)
   D1=p(1);
   D2=p(2);
   L11=p(3);
   L22=p(4);
   L12=p(5);
   
   lambdam=L11-L22;
   lambda0=sqrt(lambdam^2+4*L12^2);
   w=L11*L22-L12^2;
   
   lambda0_w=lambda0/w;
   lambdam_w=lambdam/w;
   lambda1221_w2=L12^2/w^2;
  
   U=@(h)psi(1/2+h)-psi(1/2);
   y=zeros(length(xdata),1);
   for ii=1:length(xdata)
    y(ii)=-(U(D1*xdata(ii))+U(D2*xdata(ii))+lambda0_w)/2+sqrt((U(D1*xdata(ii))-U(D2*xdata(ii))-lambdam_w)^2/4+lambda1221_w2);  
   end